ABSTRACT This is an application for a K01 award for Dr. Haesuk Park, Assistant Professor in the Department of Pharmaceutical Outcomes & Policy at University of Florida College of Pharmacy. Dr. Park is establishing herself as a young health services researcher in viral hepatitis and health policy for vulnerable populations. This K01 award will provide Dr. Park with the support necessary to accomplish the following goals: (1) gain a solid understanding of health risk factors related to hepatitis C virus (HCV) infection with emphasis on substance use disorder and human immunodeficiency virus (HIV) co-infection; (2) obtain intensive training in the development of survey instruments and conducting survey research; (3) gain further epidemiology and statistical knowledge relevant to longitudinal analysis of Medicaid claims and registry data; and (4) acquire further grant writing skills and experiences, resulting in the submission of a R01 grant before the end of the support period. To achieve these goals, Dr. Park has assembled a mentoring team comprised of a primary mentor, Dr. Robert L. Cook, Professor of Epidemiology and Internal Medicine at University of Florida, an expert on substance use and HIV infection, and three co-mentors: Dr. David L. Nelson, a hepatologist who conducts clinical investigations in effectiveness and safety of new HCV therapies including HCV-TARGET and PRIORITIZE study; Dr. Almut G. Winterstein, an expert on pharmacoepidemiology and disease risk models using claims data; and Dr. Jeff S. Harman, who has expertise in health policy and health services research in vulnerable populations. Despite effective HCV therapies now available, a majority of state Medicaid programs restrict access to new HCV therapy for persons who use substances as well as individuals co-infected with HIV. Dr. Park's current research will focus on the impact of Medicaid prior authorization policies on prescribers' practices, patient's access to the new HCV therapies, and the clinical outcomes in HCV-infected patients with substance use disorder and or HIV co-infection. This proposal has three specific aims: (1) to understand physicians' attitudes and practices toward treating HCV-infected patients with substance use disorder and/or HIV co- infection in relation to Medicaid prior authorization policies; (2) to compare treatment initiation rates among patients (i) HCV mono-infected with substance use disorder, (ii) HCV mono-infected without substance use disorder; (iii) HCV/HIV co-infected with substance use disorder; and (iv) HCV/HIV co-infected without substance use disorder using two large states (Florida and Texas) Medicaid data; and (3) for treated HCV patients, we will link the Medicaid dataset of patients with HCV-TARGET registry data to examine adherence to antiviral regimes and sustained virologic response (SVR) and investigate whether adherence and SVR are moderated by substance use disorders and/or HIV co-infection. Dr. Park will use qualitative (physician survey) and quantitative methods including linking of HCV-TARGET registry with Medicaid data. This research will form the basis for a quasi-experimental longitudinal study as well as patient survey, to be proposed in an R01 grant application before the end of the K award.